Code for 'Reverse a Vector'

101 views (last 30 days)
Capulus_love
Capulus_love on 13 Aug 2020
Commented: Rik on 25 Jan 2021
v = [1 2 3 4 5];
w = reversal(v)
%-----------------------------------------------------------
function w = reversal(v)
persistent z;
s = size(v);
e = s(2);
z(e) = v(1);
if s(2) == 1
return
end
v = v(2:end);
reversal(v);
w = z;
end
% The problem is that i can't pass the random vector.
% Error says Variable w must be of size [1 9]. It is currently of size [1 15].
% Check where the variable is assigned a value.
% Test failed using v = [ -75 -22 57 13 -34 2 -94 -49 -11]
% Why does it work like this?
  1 Comment
Atif Penkar
Atif Penkar on 23 Aug 2020
Did you solve this one? I am stuck on this too, if you could help me out would be great..

Sign in to comment.

Answers (4)

Md Jawarul Moresalein Ayon
I have done this one,you may check it ---
function w=reversal(v)
s=length(v);
if s==1
w=v;
else
w(1,1)=v(end);
v=v(1:end-1);
w=[w(1,1),reversal(v)];
end
  11 Comments
Micheal Omojola
Micheal Omojola on 9 Nov 2020
@Bruno Luong. I have edited Walter's code, and it takes care of empty input:
function y=reversal(v)
y=[];
if length(v)==1
y=v(1);
elseif length(v) > 1
k=v(1:ceil(length(v)/2));
b=v(ceil(length(v)/2)+1 :end);
y=[reversal(b) reversal(k)];
else
return
end
end

Sign in to comment.


Serhii Tetora
Serhii Tetora on 13 Aug 2020
I had no this error with
v = [ -75 -22 57 13 -34 2 -94 -49 -11]
You can also use
w = flip(v)
It is same..
  1 Comment
Capulus_love
Capulus_love on 13 Aug 2020
i have no error too... but the answer says there is a problem.
i know the function 'flip' , but it needs to use recursive function so i made it.

Sign in to comment.


Walter Roberson
Walter Roberson on 13 Aug 2020
That approach is wrong.
Reverse of A B is reverse of B, followed by reverse of A. When you let either A or B be a scalar then reverse of the scalar is the value itself. Therefore you can code each step with just a single recursive call and appending data.

xin yi leow
xin yi leow on 25 Jan 2021
function v=reversal(w)
if length(w)==1
v=w(1);
else
v=[reversal(w(2:end)) w(1)];
end
end
  1 Comment
Rik
Rik on 25 Jan 2021
Your function will fail for empty inputs. The edit below fixed that and makes the function more compact.
function v=reversal(v)
if numel(v)>1
v=[reversal(v(2:end)) v(1)];
end
end

Sign in to comment.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!